To date I haven't purchased a follow focus for my DSLR rig because of A) lack of funds, and B) I was waiting to see what the future held. Well, here's the future, courtesy Redrock Micro. FreshDV interviews Brian Valente about their wireless follow focus, which starts at $1,000 (several times less than most wireless systems, and cheaper even than many wired follow focusi). And yes, it integrates with an iPhone, although the responsiveness remains to be seen.
To reserve one, email email@example.com.